1. Field of the Invention
The present invention relates to a method for driving a plasma display panel.
2. Description of the Related Art
AC type (AC discharge type) plasma display panels (hereafter PDP) have been commercialized as slim display devices. In a PDP, two substrates, that is a front transparent substrate and a rear substrate, are disposed facing each other with a predetermined space. On the inner face (surface facing the rear substrate) of the front transparent substrate as a display surface, a plurality of row electrode pairs, which extend in the horizontal direction of the screen respectively as a pair, are formed. Also on the inner face of the front transparent substrate, a dielectric layer for coating each of the row electrode pairs, is formed. On the rear substrate, on the other hand, a plurality of column electrodes, which extend in the vertical direction of the screen so as to cross with the row electrode pairs, are disposed. If viewed from the display surface side, pixel cells corresponding to pixels are formed at the intersections of the row electrode pairs and the column electrodes.
Grayscale driving using a subfield method is performed to such a PDP so that half tone display brightness, corresponding to the input video signal, can be acquired.
In the case of grayscale driving based on a subfield method, display driving is performed for all the pixel cells of one screen in each of the plurality of subfields to which an emission count (period) is assigned respectively. In each subfield, an address process and a sustain process are sequentially executed. In the address process, an address discharge is generated according to the input video signal in each pixel cell belonging to the display line to generate (or erase) a predetermined amount of wall charges, sequentially one display line at a time. In a subsequent sustain process, a sustain pulse is applied to all the row electrodes of a PDP respectively for a number of times corresponding to the subfields, so that only the pixel cells, where a predetermined amount of wall sustain-discharge is generated repeatedly for this number of times, and an emission state generated by this discharge is maintained.
According to this driving, the time interval from the generation of a selective discharge in the address process to the generation of a sustain discharge in the subsequent sustain process differs depending on the display line. In other words, the time interval from the generation of a selective discharge to the generation of a first sustain discharge is longer in a pixel cell where the selective discharge was generated at a relatively early point of time of the address process, than in a pixel cell where the selective discharge was generated at a relatively late point of time. In this connection, charged particles generated by a selective discharge are gradually annihilated as time elapses, so it is becoming difficult to stably generate a sustain discharge having a predetermined discharge intensity in a pixel cell of which this time interval is long.
Therefore a drive method for stabilizing a sustain discharge by increasing the pulse width (pulse voltage) of the first sustain pulse to be applied in the sustain process, comparing with the second or later sustain pulses, was proposed. For example, Japanese Patent Kokai No. H07-134565 (Patent document 1) discloses such a driving method.
However if the pulse width of the sustain pulse is increased, the time spent for the sustain process increases accordingly, so it is difficult to increase the number of grayscales by increasing the number of subfields in one field display period. Also in order to increase the pulse voltage of the sustain pulse to be applied first compared with other sustain pulses, two types of different pulse voltages must be generated, which increases the circuit scale of the driver.